1. Field of the Invention
The present invention relates to a method and apparatus for electroerosive cutting of a workpiece having a wire electrode, suitable for erosive cutting, guided in at least one toroidal guide and possibly at least one main guide which is associated with the toroidal guide.
2. Description of the Related Art
Such devices which have a toroidal guide are known, for instance, from DE 42 28 331 A1. Toroidal guides are particularly suitable for conical cuts. For this, DE 42 28 331 A1 provides two wire guides, one on the top side and the other on the bottom side of the workpiece, an open wire guide--in the following also referred to as main guide--and a toroidal guide being arranged on each side of the workpiece, the toroidal guide being located between the open wire guide and the workpiece. Upon cylindrical cuts, i.e. upon cutting without conical inclination, but also in the case of cuts with a slight conical inclination, the open guide assures precise guidance of the erosion wire. Upon cuts with a larger conical inclination, the toroidal guide assumes the guidance of the wire. By this closed toroidal guidance the slipping of the erosion wire out of the open wire guide is avoided even in the case of large cone angles.
The inside diameter of the toroid and the arrangement of open wire guide and toroidal guide are so selected in DE 42 28 331 A1 that upon the cylindrical or conical cut the wire is guided up to about two degrees of inclination by the open wire guides, while in the case of a cone angle of more than two degrees, it is guided by the toroid. It is therefore of the greatest importance to control the point of contact between wire and toroid. For this purpose, it is proposed, in accordance with DE 42 28 329 A1, to measure the position of the erosion wire within or on the contour of the toroid. In this case, however, a suitable wire-position sensor is necessary on the upper toroid and the lower toroid.